The goal of this work is to study how cells in the Drosophila embryo are directed to form specific pattern elements within each segment. We have chosen three loci (odd-skipped, armadillo and orthodenticle) which seem to identify three different levels in the process. We have cloned two of these genes and have obtained a molecular entry into the third using its proximity to a previously cloned inversion breakpoint. In our earlier work, we have characterized mutations at each locus in homozygous embryos and in imaginal disc clones. The long-range goal of the present project will be to relate this detailed information to the transcriptional activities of these three genes and to develop a molecular model for their function based on their sequence and the intracellular localization of their protein products. After an initial characterization of the cloned sequences has been completed and candidate transcripts have been identified, we will use P-element mediated transformation to unambiguously define the genomic region required for each function. Radiolabelled probes from each gene will be in situ hybridized to sectioned embryos and imaginal discs, in order to identify regions of localized gene activity. Wild type patterns of transcript accumulation will be compared to those in various mutants, and the epistatic relationships between the three loci and their interactions with other segmentation genes will be analyzed. Gene fusions will be constructed to identify cis-controlling regions and to allow isolation of peptide sequences form each gene for use in the synthesis of polyclonal and monoclonal antibodies.